We will take advantage of the texternal and internal heavy atom effect to study the interaction of heavy atom probes with biopolymers, bacteriophages, and whole cells. Spectroscopic methods will be used, and will include most prominently the study of luminescence, phosphorescence decay kinetics including their wavelength dispersion, and triplet state optical detection of magnetic resonance (ODMR) in zero field. The heavy atom effect enhances the intersystem crossing quantum yield of a luminescent molecule, reduces the triplet lifetime, and often enhances the triplet radiative quantum yield. Time resolved ODMR methods will be used to selectively enhance the signals from perturbed molecules and allow us to identify the close approach (within the van der Waals' radii) of a heavy atom to a luminescent molecule. Among the naturally occurring luminescent molecules of biological systems which are subject to heavy atom effects are tryptophan, tyrosine, and the nucleotide bases. The characteristic zero field splittings and perturbed triplet lifetimes will be used to identify the direct interaction with a heavy atom in biological systems. Methylmercury(II), which is known to complex with each of the molecules mentioned above and to produce a heavy atom effect will be used as a heavy atom perturber of polynucleotides, enzymes, bacteriophages, and whole cells in many of the proposed investigations. In studies of aromatic interactions accompanying the binding of DNA with DNA-binding proteins and enzymes, heavy atom derivatized DNA will be employed as a perturber. 5-mercuri-UTP will be used as a heavy atom substrate to study the ternary complex of RNA polymerase, DNA, and RNA. In order to aid in the identification of perturbed molecules in complex systems containing multiple emissions, we propose to develop the method of amplitude modulated phosphorescence-microwave double resonance to isolate the phosphorescence spectra of individual heavy atom perturbed triplet states.